The present invention relates to a digital oscilloscope capable of simultaneously displaying a plurality of waveforms and capable of performing various operations with respect to an operator-selected one of the displayed waveforms, and in particular to a method and apparatus for permitting an oscilloscope operator to control waveform selection.
Many digital oscilloscopes can simultaneously display several waveforms, each representing the magnitude of a different input signal as a function of time. Such oscilloscopes permit an operator to adjust various display attributes of each of the waveforms including for example, its vertical position on the oscilloscope's screen, the scaling of its vertical size, its trigger level, its color, its intensity, etc. Since each waveform may have several adjustable display attributes and since several waveforms may be displayed, it may be impractical to provide a separate front panel knob or switch for controlling each attribute of each waveform. Some oscilloscopes provide a separate knob or switch for controlling each display attribute and a set of pushbuttons or a rotary knob for permitting an operator to "select" a particular one of the displayed waveforms. In order to change a display attribute of a particular waveform, an operator first selects the waveform using the waveform selection knob or pushbuttons. Once the waveform is selected, the oscilloscope reconfigures itself so that it responds to operation of any of the waveform attribute control knobs or buttons by changing display attributes of the selected waveform.
Other oscilloscopes eliminate the need for dedicated waveform selection knobs or pushbuttons by permitting the operator to select a waveform from a list of waveforms on a "waveform selection" menu displayed on the screen. With some menu-based oscilloscopes, an operator indicates his selection by depressing a particular one of a set of menu item selection pushbuttons, often mounted on the oscilloscope near the screen. While such oscilloscopes still require the use of pushbuttons for waveform selection, the pushbuttons may be used for other purposes when other menus are displayed. Some menu-based instruments have "touchscreen" input systems which sense when an operator has touched an instrument screen and provide input data to the instrument indicating the screen coordinates of the touch. Such touchscreen instruments permit an operator to make selections from a displayed menu by directly touching a selectable menu item, thereby eliminating the need for menu item selection pushbuttons.
Some digital oscilloscopes also include provisions for assisting an operator in making various measurements with respect to an operator-selected waveform. For example, an oscilloscope may determine and display data representing the magnitude of any point on a selected waveform indicated by an operator controlled cursor, may determine the minimum and maximum magnitudes of a selected waveform between two points indicated by a pair of operator controlled cursors, or may show an operator-determined portion of a selected waveform in expanded horizontal scale. By permitting an operator to "select" the waveform upon which such measurements are to be performed, the need for separate pushbuttons, control knobs and other input devices for separately controlling measurement parameters for each displayed waveform is eliminated.
Thus by providing the operator with the ability to "select" a displayed waveform for purposes of directing the response of the oscilloscope to operator manipulation of various pushbuttons, knobs or other input devices which control waveform display attributes or waveform measurement parameters, the number of such input devices needed to control the oscilloscope can be reduced. However, requiring the operator to select a waveform before using such devices to manipulate waveform display attributes or measurement parameters adds complexity to what the operator must know and do in order to adjust an oscilloscope operation. For example, in the case of a menu-based system, he must first cause the oscilloscope to display the waveform selection menu and he must select a waveform from the menu once displayed. In some systems he must also cause the oscilloscope to remove the menu from the screen once the selection is made. These extra steps increase the time required for an operator to change waveform display attributes or measurement parameters. The additional steps can also lead to more frequent human error because it is not always easy to determine which waveform corresponds to a particular waveform selection menu item when the operator is free to alter the order in which waveforms are displayed on the oscilloscope screen.
What is needed is a system permitting an operator to provide input to a digital oscilloscope indicating an operator's selection of a waveform, wherein the system is easy to understand and use.